Anchorage length is an integral part of the design of embankments on piles over soft foundation soils, as part of a foundation system to control stability and prevent or limit settlement of the embankment. In these projects high strength geosynthetic reinforcement is placed at the base of the embankment, directly over the pile caps, where they support all or part of the vertical stress applied on the foundation soil through the tensioned membrane mechanism. The geosynthetic reinforcement has to carry high tensile forces, which can occur only if the geosynthetic reinforcement is properly anchored at the extremities of the embankment. Hence there is a need to design and construct adequate anchorage lengths. The anchorage length can be provided as a straight length, or more commonly by wrapping the geosynthetic reinforcement around gabions placed at the toe of the embankment. This paper presents a new, more rigorous, design method for determining the anchorage length of geosynthetic reinforcement in embankments with basal reinforcement supported on piles. The required anchorage length for the geosynthetic reinforcement is calculated considering the long-term (unfactored) tensile strength in the geosynthetic reinforcement, and all the resisting forces (pullout force on pile cap, pullout force between gabion and first pile cap, pullout forces over and below gabions, pullout force along anchorage length). The long-term (unfactored) tensile strength in the geosynthetic reinforcement, the load on piles and the load under arching between piles must be calculated in advance, using either Marston’s or the Hewlett & Randolph methods (BS 8006-1:2010+A1 (2016) ). A new Factor of Safety for anchorage length can be defined as the ratio of the total pullout resisting force mobilized along the full length of the geosynthetic reinforcement beyond the outer pile cap to the long-term (unfactored) tensile strength required in the geosynthetic reinforcement. In the proposed method the anchorage length is determined by trial and error until the calculated Factor of Safety for anchorage exceeds the minimum required value. A design example is provided to show the potential of the method.
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